U.S. patent number 5,698,082 [Application Number 08/746,437] was granted by the patent office on 1997-12-16 for method and apparatus for coating substrates in a vacuum chamber, with a system for the detection and suppression of undesirable arcing.
This patent grant is currently assigned to Balzers und Leybold. Invention is credited to Jurgen Bruch, Gotz Teschner.
United States Patent |
5,698,082 |
Teschner , et al. |
December 16, 1997 |
Method and apparatus for coating substrates in a vacuum chamber,
with a system for the detection and suppression of undesirable
arcing
Abstract
In an apparatus for coating substrates, having sputtering
cathodes (4, 5) disposed in a vacuum chamber (1), sputtering
targets (6, 7), a medium-frequency generator (9) connected to the
cathodes (4, 5), and a system (16) for detecting and suppressing
undesired arcing, a cycle of the medium-frequency signal of the
medium-frequency generator (9) is divided into a plurality of time
segments, the electrical values of current and voltage for a
predetermined time segment being determined so as to form a
measured value signal and being entered into a ground-free meter
island (16). The meter island (16) is tied as a remote station into
a circular network (9, 16, 17, 18, 19, 11) whose master station is
situated in the control unit (11) present in the generator (9). The
blocking of the generator (9) when an arc occurs takes place
through a line (19) connecting the meter island (16) to the
generator (9). The parameters of the arc surveillance and the
detection of measured values are preset through the network (17,
18, 19) by means of software.
Inventors: |
Teschner; Gotz (Gelnhausen,
DE), Bruch; Jurgen (Hammersbach, DE) |
Assignee: |
Balzers und Leybold (Hanau am
Main, DE)
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Family
ID: |
25928313 |
Appl.
No.: |
08/746,437 |
Filed: |
November 8, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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283788 |
Aug 1, 1994 |
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Foreign Application Priority Data
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Aug 4, 1993 [DE] |
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43 26 100.0 |
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Current U.S.
Class: |
204/298.03;
204/192.13; 204/298.08; 204/298.26 |
Current CPC
Class: |
H01J
37/34 (20130101); H01J 37/3444 (20130101); H01J
2237/0206 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); H01J 37/34 (20060101); C23C
014/34 () |
Field of
Search: |
;204/192.12,192.13,192.22,298.08,298.03,298.26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0546293 |
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Jun 1993 |
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EP |
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0544107 |
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Jun 1993 |
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EP |
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2226666 |
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Dec 1973 |
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DE |
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2550282 |
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May 1977 |
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DE |
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3925047 |
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Jan 1991 |
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DE |
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4033856 |
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Jul 1991 |
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DE |
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4104105 |
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Aug 1992 |
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DE |
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4134461 |
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Apr 1993 |
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DE |
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4138793 |
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May 1993 |
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DE |
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4200636 |
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Jul 1993 |
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DE |
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4204999 |
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Aug 1993 |
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DE |
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4204998 |
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Aug 1993 |
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DE |
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Other References
G Jackson, "Electrical . . . discharge", Vacuum/vol. 21/No. 11, pp.
533-543..
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Primary Examiner: Nguyen; Nam
Attorney, Agent or Firm: Felfe & Lynch
Parent Case Text
This application is a continuation-in-part of U.S. Ser. No.
08/283,788 filed Aug. 1, 1994, now abandoned.
Claims
What is claimed is:
1. Apparatus for coating substrates with an electrically
non-conductive coating in a reactive atmosphere, said apparatus
comprising
a vacuum chamber having a process gas inlet,
a pair of sputtering cathodes located in said vacuum chamber, said
cathodes carrying targets consisting of a material to be
sputtered,
a medium frequency generator connected to said cathodes by a pair
of conductors, said generator having a cycle separated by voltage
nulls and divided into a plurality of time segments, said generator
comprising a programmable storage controller which forms threshold
values of voltage and current for detection of arcs,
a compensated symmetrical voltage divider connected between said
pair of conductors for determining a voltage value,
a current converter looped into one of said conductors for
determining a current value,
an ungrounded meter island which samples said voltage and current
values during predetermined said time segments and forms measured
value signals based on said sampled voltage and current values,
a feedback network for transmitting said measured value signals to
said programmable storage controller, and for transmitting said
threshold values back to said meter island,
means in said meter island for detecting an arc based on measured
value signals and said threshold values, and for producing a
blocking signal based on at least one said arc, and
a connecting line connecting said meter island to said medium
frequency generator for blocking said generator for a predetermined
time when said blocking signal is received.
2. Apparatus as in claim 1 further comprising
a capacitor between said cathodes,
a compensation winding in said current converter, said compensation
winding being connected between said pair of conductors, and
a capacitor between said compensation winding and said conductor
into which said converter is not looped.
3. Apparatus as in claim 1 wherein said feedback network and said
connecting line consist of light pipes.
4. Apparatus as in claim 3 further comprising an isolation
transformer which supplies voltage to said meter island.
5. Apparatus as in claim 1 wherein said meter island comprises
a trigger which receives said voltage and current values as analog
inputs, and generates processed signals,
an analog to digital converter which converts some of said
processed signals to digital signals,
an arc logic circuit-which also receives some of said processed
signals,
a synchronization and timing unit which synchronizes said analog to
digital converter to said arc logic circuit, and
a microprocessor which communicates with said analog to digital
converter, said arc logic circuit, and said synchronization and
timing unit, said microprocessor forming said measured value
signals and transmitting said measured value signals to said
programmable storage controller.
6. Apparatus as in claim 5 wherein, said trigger comprises
input amplifiers which receives said analog inputs and produces
analog outputs, and
quantifiers which receive said analog outputs from respective said
input amplifiers to produce quantified values for voltage and
current, said quantified values being used as threshold values.
7. Apparatus as in claim 1 wherein said means for detecting an arc
determines that an arc is present when the voltage value is below a
threshold voltage value and the current value is above a threshold
current value.
8. Apparatus as in claim 1 wherein said means for producing a
blocking signal only produces a blocking signal when the number of
detected arcs exceeds a preset value.
Description
BACKGROUND OF THE INVENTION
The invention relates to a method and an apparatus for coating
substrates, especially with electrically nonconductive coatings in
a reactive atmosphere, the apparatus having sputtering cathodes
disposed in a vacuum chamber which has a gas inlet, sputtering
targets consisting of the material to be sputtered, a
medium-frequency generator connected to the cathodes by a double
conductor, and a system for the detection and suppression of
undesired arcing.
A method and an apparatus are described in U.S. Pat. No. 5,169,509
for the reactive coating of a substrate with an electrically
insulating material, silicon dioxide (SiO.sub.2), for example; it
consists of an alternating-current source connected to cathodes
enclosing magnets which are disposed in a coating chamber and
cooperating with targets, two ungrounded outputs of the
alternating-current source being connected each to a cathode
bearing a target, both cathodes being placed side by side in a
plasma space in the coating chamber, and having each approximately
the same distance apart from the substrate opposite it. The
effective value of the discharge voltage is measured by an
effective voltage detector connected to the cathode by a conductor
and applied through a conductor as direct current to a regulator
which controls the flow of reactive gas from the tank into the
distribution line such that the voltage measured agrees with a set
voltage.
An apparatus for the reactive coating of a substrate is also
described in U.S. Pat. No. 5,240,584 (related to U.S. Pat. No.
5,126,032) in which a cathode that comprises two parts electrically
separated from one another and from the vacuum chamber and is
configured as a magnetron cathode, wherein the base body of the
target, with its yoke and magnet, is connected through a capacitor
to the negative pole of a direct-current voltage source, and to the
power supply through a choke and a resistor parallel thereto, and
wherein the target is connected through another capacitor to the
plus pole of the power supply and to the anode which in turn is
connected to ground through a resistor; an inductance is inserted
in series with the low-induction capacitor and with the choke, and
the value of the resistor is typically between 2 K.OMEGA. and 10
K.OMEGA.. This patented apparatus is already so configured that it
suppresses most of the arcing that occurs during a coating process
and lowers the energy of the arcs, and it improves the reignition
of the plasma after arc.
SUMMARY OF THE INVENTION
The present invention is addressed to the problem of creating a
system for early arc detection and suppression for coating
apparatus of special size and power, which will permit the
operating personnel to adjust the apparatus such that only the arcs
that are harmful for a particular coating process will be
suppressed.
This problem is solved in accordance with the invention by the fact
that a half cycle of the medium-frequency signal of the
medium-frequency generator is divided into a plurality of time
segments, and for a predetermined time segment the electrical
values of current and voltage for the formation of a set-voltage
signal are detected and put into a meter island. For this purpose
the voltage is determined through a compensated symmetrical voltage
divider that is connected between the two cathodes and the current
is determined through a converter which is looped into the lead of
one cathode. The meter island is tied as a remote station into a
feedback network, the master station of which is located in a
control unit present in the generator and configured as a
programmable storage controller. Blocking of the generator takes
place whenever an arc occurs, through a connecting line which
connects the meter island to the generator. For this purpose the
parameters of the arc surveillance and value determination are
preset via the network by means of software, e.g., by a
programmable storage controller.
The reactive sputtering processes used preferentially in the
apparatus in question show a hysteresis-affected dependency of the
discharge voltage on the reactive gas content. Due to the steep
characteristic at the working point they have a tendency even at
slight fluctuations of the process parameters to tilt into another
state, but one which is not appropriate for the process. A stable
management of the process requires, among other things, that the
power fed by the medium-frequency generator into the cathodes be
constant. Therefore it is necessary to measure voltage and current
at the cathodes as primary signals and from them to determine the
power value by multiplication. The peak present in the voltage is
dependent on the ignition performance in the system, which is
affected by the type and pressure of the gas. This area is not
important to the actual sputtering process, but it does
considerably influence the average and effective voltage. If these
factors would be used as a measure of the discharge voltage, then
fluctuations in the ignition performance, due to pressure
instabilities for example, would falsely indicate a variation in
the actual discharge voltage. The latter is determined by the
signal area (discharge area) adjoining the ignition peak. The area
that is characteristic of the discharge and thus for the process
can exhibit different curves, depending on the process set-up, so
that it is useful, depending on the process used, to take into
account different portions of the signals to establish the actual
level.
To be able to judge and document certain process states it is
necessary to learn the characteristic signal curves, for example
with a recorder. The signals, however, must be appropriately
processed, since ordinary recorders are unable to image signals in
the frequency range in question (40 kHz, for example).
On account of the cathode capacity itself as well as any condensers
that may be connected directly to the cathode, the measured current
contains a quadrature component that has to be compensated by
appropriate measures.
In sputtering with a reactive gas, flashovers occur in various
forms which are usually called sparks. Sparking occurs on targets
between regions that are occupied by an insulating coating and
regions which are metallically clean, as an equalization of charges
in the form of small flashes of light. Furthermore, short-circuits
of the cathodes and/or targets occur between one another and
between the cathodes and/or targets and other parts of the
sputtering apparatus. Flashovers can interfere with the sputtering
process and damage the target surface. Most of these flashovers are
of low energy and extinguish by themselves without further ado.
However, higher-energy flashovers also occur, which persist and
form arcs and, if they are not quickly extinguished, lead to severe
damage preventing the continuation of the process. To be able to
react appropriately to these different flashovers it is necessary
to develop methods for their reliable recognition and permitting
the quick extinction of arcs. FIG. 3 is a qualitative
representation of the curve of a typical spark (5th cycle).
The dual cathode system supplied with medium frequency is, as a
rule, closed without grounding for reasons of symmetry. The maximum
voltage occurring between the two cathodes is on the order of 1 . .
. 2 kV. The potential difference between cathode and ground is of
the same order of magnitude. So it is necessary to find a suitable
method for measuring the voltage between the cathodes and the
current passing through them.
Since different methods and processes are used in an existing
apparatus, the possibility must be provided for a very flexible
control of the arc logic and of the measurement in order to provide
for the various requirements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 the basic arrangement of the components of the
apparatus,
FIG. 2 a diagrammatic representation of the relationship between
the reactive gas content and the medium-frequency power,
FIG. 3 typical curves for the cathode voltage and cathode
current,
FIG. 4 a diagrammatic representation of cathode voltage and cathode
current and the division into individual time segments,
FIG. 5 a diagrammatic representation of arcing on one side (cathode
against surroundings), wherein the arc counter is set at 3 and the
arc counter reset is performed after two intact cycles,
FIG. 6 a representation of symmetrical arcs (between two cathodes),
wherein the arc counter is set at 3 and the arc counter reset is
performed after two intact cycles,
FIG. 7 a representation of the functional groups of the electronic
MAM microprocessor (MAM=medium-frequency arc logic signal
detector),
FIG. 8 a representation of the analog inputs and of the trigger
according to FIG. 7,
FIG. 9 a representation of the components for synchronization and
timing,
FIG. 10 a representation of the component of the arc logic of FIG.
7,
FIG. 11 a representation of the analog-to-digital converter of FIG.
7, and
FIG. 12 a representation of the microprocessor of FIG. 7.
The apparatus consists essentially of the coating chamber 1 with
the vacuum pump connection 2 and the gas inlet 3, and with the
cathodes 4 and 5 disposed in the chamber with the corresponding
targets 6 and 7, the substrate 8, the medium-frequency generator 9
connected by the coaxial cable 10 to the control 11, the voltage
divider 12, the current converter 13 with compensation winding 20,
the two capacitors 14 and 15, the medium-frequency arc logic signal
detector 16 with isolation transformer 21 and the light pipes 17,
18 and 19 which connect the generator 9 and control 11 to the
circuit 16. The circuit is in turn further represented in FIGS. 7
to 12, and consists essentially of the analog-to-digital converter
23, the component 24 for synchronization and timing, component 25
for the arc logic, the microprocessor 26 and the component 22 with
analog inputs and trigger.
An important feature of the invention is that a cycle of the
medium-frequency signal is divided into 10 time segments, for
example, (see FIG. 4). By the appropriate selection of such a time
segment and the detection of the currents and voltages present in
this instant it is possible to employ the signal segment best
suited for a controlling action, and only that segment, for the
formation of the measured value signal. In FIG. 4 such a segment is
identified by R. To monitor arcing, the signals are examined in
another segment more appropriate for this purpose (marked A in FIG.
4). Furthermore, the signal levels in the individual segments can
be scanned successively at a slow frequency (sampling method) and
thus a low-frequency signal can be generated which has the
characteristic curve of the medium-frequency signal (marked M in
FIG. 4) and can be represented on a conventional recorder. The
signals needed for the resolution of the cycle are synchronized by
the nulls of the voltage signal.
An arc is characterized by the fact that the voltage drops to a low
level (the arc voltage), while at the same time the current remains
at its high level or is still rising. Checking for such a state
takes place in each cycle, in a section suitable for the purpose,
as mentioned in the previous paragraph. If at the instant in
question the voltage level is below a threshold U.sub.arc and the
current level is higher than another threshold I.sub.null, this is
an arcing state. The arc signals are counted, this being done in as
many as three separate event counters, one of which counts all of
the arcs that occur, the next all that occur in the positive cycle,
and the third all that occur in the negative cycle. In this manner
the different symmetrical and unsymmetrical arcs can be evaluated
separately. If these counters reach certain states preset by
selector switches or by software from the PROM, a signal is
produced which blocks the generator for a definite time which can
be set by selector switch or by software. Then the arc monitoring
is suppressed for a definite time which can be set by selector
switch or by software, in order to prevent erroneous reactions due
to re-entry oscillation when the power returns. By means of an
additional counter, which is set back by every occurring arc, the
number of successive intact cycles is counted, in which no arc
state is detected. When this counter reaches a state preset by
selector switch or by software the actual arc counter is reset,
since it can be assumed that a previously occurring persistent arc
has been extinguished. In FIGS. 5 and 6 a number of examples of arc
monitoring are represented, and in this case only a single arc
counter is assumed, which counts all the flashovers that occur.
The voltage is measured by a compensated symmetrical voltage
divider 12 which is connected between the cathodes 4 and 5. The
current is measured through a converter 13 which is looped into the
feeder of a cathode. To compensate for the wattless currents
through the converter directly at the capacitors 15 that are
present, a compensating winding 20 is applied through which a
capacitive compensation current can flow through the condenser 14
in the opposite direction through the converter.
The measurement is performed on an ungrounded meter island 16 which
is housed in the immediate vicinity of the cathodes 4 and 5 and is
at the center cathode potential. The signals are transferred from
and to this island by light pipes. Power is supplied from an
appropriately isolated transformer 21.
The meter island 16 is connected as a remote station to a feedback
network 17 and 18 whose master station is located in the control 11
(e.g., PROM) present in the generator. The signal reading is
controlled through this light pipe connection and the data are
transferred from the meter island 16 to the control 11. The
blocking of the generator in case of an arc is performed through a
separate light pipe 19 connection permitting a fast reaction.
All the essential parameters of the arc surveillance and signal
detection are supplied through the network by software, e.g., by a
PROM.
The apparatus described uses only the relevant areas within the
medium-frequency cycle for the control and stabilization of the
process. This signifies a considerably more reliable operation of
the process than in the case of the solutions known heretofore,
which relate to the average and effective values of the signals.
Detecting the signal levels directly at the cathodes prevents
signal distortions, and the isolation problems they raise are
solved by the use of light pipes. Due to controlling via a
bidirectional network connection the signal detection system can be
configured in an extremely flexible manner, since the arc
surveillance and signal processing can be parametered by software.
Arcing is securely recognized and rapidly quenched.
The example given is based on the scheme represented in FIG. 1. The
medium-frequency generator 9 has a frequency of 40 kHz. The parts
essential to the invention are the electronic-chip MAM 16, which is
supplied through an isolation transformer 21 and to which the
measured value signals of the cathode current and cathode voltage
are fed through the current converter 13 and the voltage divider, a
compensation circuit 14 and 20 and the light pipe connections 17,
18 and 19 which connect the electronic chip to the medium-frequency
generator 9 and the PROM 11.
FIG. 7 gives an overall view of the different functional groups of
the MAM electronic chip and meter island 16, wherein the I.sub.K
and U.sub.K taken from the cathode power source flows into the
input component 22, whose processed signals then flow through
components 23, 24 and 25 to the microprocessor 26 and from there to
the generator 9. In FIGS. 8 to 12 the individual circuit components
are shown in greater detail, the direction of current flow being
indicated by arrows.
______________________________________ Unit Circuit member type
______________________________________ 27. Differential input
(BUF03, HA2525) amplifier 28. Input amplifier (HA2525) 29.
Comparator (LM319) 30. Comparator (LM319) 31. Comparator (LM319)
32. Rectifier (TL084) 33. Rectifier (TL084) 34. Timer (XO5860) 35.
Decimal counter (74HCT4017) 36. 4-bit BCD counter (74HCT190) 37.
Digital comparator (74HCT85) 38. Digital comparator (74HCT85) 39.
Programmable 4-bit down-counter (74HCT190) 40. Programmable 4-bit
down-counter (74HCT190) 41. Programmable 4-bit down-counter
(74HCT190) 42. Programmable 4-bit down-counter (74HCT190) 43. 1
kiloHerz square-wave generator (74HCT04) 44. 6-bit binary counter
(In 80C31) 45. Timer 1 (74HCT191) 46. Timer 2 (74HCT191) 47. LWL
Transmitter (DC9003P) 48. 12-bit A/D converter (ADS7800) 49. 12-bit
A/D converter (ADS7800) 50. Input-Output Interface (74HCT573,
74HCT574, 74HCT245) 51. CPU (CENTRAL PROCESSING UNIT) (8OC31) 52.
EPROM (ERASABLE, (27C256) PROGRAMMABLE READ-ONLY MEMORY) 53. RAM
(RANDOM ACCESS MEMORY) (HM6264) 54. Chip-select logic (74HCT138)
55. Gate array (AGMA-M32) 56. Gate array (AGMA-M32) 57. Receiver
(DC90003P) 58. Transmitter (DC9003P)
______________________________________
FIG. 8 is a detailed layout of the arc input and trigger component
22 depicted in FIG. 7. The actual measured values U.sub.K and
I.sub.K are amplified by input amplifiers 27 and 28, the current
value I.sub.K being transformed to a proportional voltage signal
U.sub.IIST. The amplified values U.sub.IST and U.sub.IIST are fed
to respective rectifiers 32, 33, as well as to the A/D converter
23. The rectified output signals .vertline.U.sub.IST .vertline. and
.vertline.U.sub.IIST .vertline. are fed to respective comparators
30, 31, where they are compared to threshold values
U.sub.THRESH-UARC and U.sub.THRESH-INULL. The threshold values are
adjusted by the values of the resistances in voltage dividers
VR.sub.U and VR.sub.I. The values U.sub.THRESH-UARC and
U.sub.THRESH-INULL are chosen according to the specific discharge
conditions, which depend on parameters of the sputtering process.
To summarize, the threshold values are preset by choosing the
appropriate resistances for the voltage dividers, according to the
plasma process being used.
The function of the programmable storage controller 11 is to
provide threshold values generally, such as preset counter limits
and preset gate times for sampling the measured voltages in the
periods R, M, and A of FIG. 4. These preset threshold values are
transmitted to the meter island 16 by light pipe 18, but for the
threshold values U.sub.THRESH, which are determined internally in
element 22. Measured data are transmitted from element 16 to
element 11 via light pipe 17, this data representing (for example)
the discharge conditions. The current and voltage values
transformed by the A/D converters shown in FIG. 11 are not used as
thresholds for arc detecting. These values are only used to monitor
the discharge over the longer term.
* * * * *